Insulation strength of wire and cable refers to the ability of insulation structure and insulation material to withstand electric field without breakdown damage. In order to check the quality of wire and cable products and ensure that the product can operate safely, insulation strength tests are generally required for all types of insulation Aluminum Concentric Cable . Dielectric strength test can be divided into withstand voltage test and breakdown test.
The withstand voltage test is to apply a certain voltage to the test product under certain conditions, and after a certain period of time, whether a breakdown occurs is used as the criterion for judging whether the test product is qualified. The time voltage is generally higher than the rated working voltage of the test product. The specific voltage value and withstand voltage time are stipulated in the product standard. The withstand voltage test can test the reliability of the product running under the working voltage and find the seriousness of the insulation Defects, some shortcomings of the production process can also be found, such as: the insulation has serious external damage, the conductor has serious defects that cause the electric field to be sharply distorted; the insulation has penetrating defects or large conductive impurities in the production.
The breakdown test is to measure the breakdown field strength or breakdown voltage under certain test conditions and increase the voltage until the test product breaks down. Through the breakdown test, the safety margin between the cable's ability to withstand voltage and the working voltage can be assessed. The breakdown field strength is one of the important parameters in cable design.
Cables generally bear AC voltage during operation, but DC power transmission systems and some special occasions also bear DC voltage. High-voltage cables may also be attacked by atmospheric voltage (lightning) and operating overvoltage. Therefore, according to the different experimental voltage waveforms, it can be divided into 1. AC (power frequency) voltage, 2. DC voltage, and 3 impulse voltage insulation strength tests.
Partial discharge measurement
For oil-filled cables, there is basically no local power generation; even if the oil-paper cables have partial discharges, they are usually very weak, such as several PCs. Therefore, these cables may not be tested for partial discharges in the factory test. For extruded cables, not only the possibility of partial discharge is high, but the damage to plastic and rubber by partial discharge is also serious. With the increase of voltage level and the increase of working field strength, this problem becomes more serious. Extruded cables must be measured for partial discharge in the factory test.
There are many methods for measuring partial discharge. The discharge pulse can be measured based on the instantaneous charge exchange generated by the discharge (electrical measurement method); the voltage can also be measured based on the ultrasonic wave generated during the discharge (acoustic measurement); and it can also be measured based on the light generated by the discharge. , Measure the intensity of light (photometry). Basically, electrical measurement methods are used for cables.
Aging and stability test
The aging test is a stability test that can maintain stable performance under the action of stress (mechanical, electrical, thermal).
Thermal aging test
A simple thermal aging test is to test the aging characteristics of the test product under the action of heat. The test product is placed in an environment with a certain temperature higher than the rated working temperature. After a specified period of time, the sensitivity of certain sensitive properties before and after aging is measured. Changes to evaluate the aging characteristics. It is also possible to increase the temperature to accelerate the aging of the test sample, plus the heat, mechanical, and electrical stresses such as moisture, vibration, and electric field to form an aging cycle. After each aging cycle, certain selected sensitive performance parameters are measured. Until the performance drops to the value of the recognized life. In this way, at a higher temperature T, a shorter lifetime L (time for heating the sample) is obtained.
Thermal stability test
The thermal stability test is that the cable is heated by current while also withstanding a certain voltage. After a certain period of heating, certain sensitive performance parameters are measured to evaluate the stability of the insulation.
Insulation stability test is divided into long-term stability test or short-term accelerated aging test.